Lithium polymer batteries use a solid electrolyte comprising a polymer and a lithium salt to separate the positive electrode from the negative electrode and to provide ionic conductivity between the electrodes. The negative electrode may be a lithium or lithium alloy metal sheet or an active material capable of insertion and deinsertion of lithium ions such as carbon or Li4Ti5O12 in a polymer binder while the positive electrode consists of electrochemically active material particles such as LiFePO4, LiMnO2, LiMn2O4, etc., an electronically conductive additive and a solid polymer electrolyte which acts as a binder as well as provides the required ionic path between the electrochemically active material particles of the positive electrode and the electrolyte separator.
Contrary to lithium ion batteries which use a liquid electrolyte and therefore the electrodes of a lithium ion electrochemical cell must be porous to allow the liquid electrolyte to soak the electrodes in order to provide the ionic path between the electrochemically active material and/or insertion material of the electrodes and the electrolyte separator, the electrodes of a lithium polymer batteries must have a very low porosity since the binder of its electrodes acts as an ionic conductor and there is no need for any porosity as in the electrodes of a lithium ion electrochemical cell.
The electrodes of a lithium polymer electrochemical cell are preferably loaded with the maximum amount of electrochemically active material particles to obtain the maximum energy density and therefore are preferably compacted to the maximum. Any porosity in the electrodes becomes wasted space and reduces the energy density of the lithium polymer electrochemical cell.
To achieve maximum compaction of the electrodes, the particle size distribution (PSD) of the electrochemically active material is important as described US patent application No. 2010/0273054 which is herein incorporated by reference, and furthermore, in a coating process wherein the particles are in suspension in an aqueous solution and/or an organic solvent, an ideal PSD is necessary but not sufficient to achieve maximum compaction and low porosity of the electrodes as a phenomenon of inter-particles repulsion comes into play that prevent maximum compaction of the electrodes
Therefore, there is a need for an electrochemically active material in which the inter-particles repulsion forces are reduced to a minimum.